JP3228740B2 - Power amplifier - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates generally to power amplifiers, and more particularly to power control ranges and amplitude modulation (A) of power amplifiers.
I) Regarding improvement of output.

BACKGROUND OF THE INVENTION The use of power amplifiers to transmit radio frequency signals
It has numerous uses, including but not limited to wireless telephone communication systems. When a power amplifier is used in a wireless telephone, (1) a large power control range,
Certain qualities of the power amplifier are desired, including (2) temperature stability, (3) current efficient signals, and (4) minimal AM output.

The entire power control range is limited at the high end by the amplifier gain at the maximum bias current, and at the low end the power control range is from the radio frequency (RF) input when the bias current is zero. Of the amplifier. Within this range, the output power is roughly proportional to the square of the bias current.

Typically, a Class C amplifier is used for maximum gain and efficiency for a given bias current. In conventional class C amplifier configurations, in the absence of a bias current, isolation from the RF input was limited by the parasitic capacitance between the transistor's collector and base.

To obtain the desired temperature stability in a low efficiency amplifier, a resistor is coupled from the emitter of the transistor contained in the amplifier to ground. This resistor stabilizes the amplifier over temperature, which is undesirable because it reduces the efficiency of the amplifier. To obtain high efficiency of the amplifier, the collector and the emitter must avoid lossy resistive elements. While the elimination of these lossy elements increases the voltage gain and efficiency of the amplifier, it makes the amplifier extremely temperature sensitive unless other bias stabilization measures are used.

FIG. 3 shows a commonly used circuit configuration for an RF power amplifier. At the center of the circuit is a bipolar transistor 309 with a common emitter configuration. The circuit attempts to obtain bias control and temperature stability by using a clamp diode 305. The inherent characteristics of this clamp diode 305 match the base-emitter junction of transistor 309. The diode voltage tends to follow the base-emitter voltage of transistor 309, producing a stable bias current for temperature that is approximately proportional to control voltage 301. The clamp diode 305 also acts as a protection for the circuit from the extra control voltage 301.

The amplifier of FIG. 3 has typical control and AM characteristics as shown in FIG. The control characteristic is a plot of the RF output power 501 over the control voltage range 301. The AM characteristic is a plot of percent AM output 503 versus 1 percent AM input at the RF signal input over control voltage range 301. The peak of the AM characteristic 503 tends to coincide with the steep part of the control characteristic 501.

If the two amplifiers shown in FIG. 3 are cascaded and the control voltage inputs are connected together directly, the composite control characteristic will have approximately twice the slope of the individual control characteristic 501. The magnitude of the AM characteristic will be approximately twice that of the individual AM characteristic 503. Increased AM performance is undesirable because AM modulation causes power fluctuations in the RF output signal 313.

There are no lossy elements in this circuit, so
Allows for maximum voltage gain and efficiency of the amplifier. However, the RF from the amplifier in the absence of bias current
The signal isolation depends on the parasitic capacitance of the transistor 309. Therefore, the power control range is not maximized.

Therefore, the need for a temperature-stable, power-efficient RF power amplifier with a large power control range and minimal AM power depends.

SUMMARY OF THE INVENTION The present invention includes an amplifier that includes a first input signal, a first output signal, a bias current, and a control voltage. The first
Carry the first radio frequency signal. The first output signal carries an amplified first radio frequency signal. Variations in the bias current are responsive to variations in the control voltage. The amplifier has means for amplifying the first input signal. The amplifier also has means for stabilizing the bias current in response to changes in temperature and means for attenuating the first radio frequency signal in response to changes in a control voltage contained within the same element. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a wireless telephone communication system in which the present invention can be used.

FIG. 2 is a block diagram of a power amplifier and a corresponding power amplifier control circuit that can use the present invention.

FIG. 3 shows a power amplifier control circuit included in the prior art.

FIG. 4 shows a two-stage power amplifier circuit to which the present invention can be applied.

FIG. 5 shows the control characteristics and the AM characteristics of the power amplifier included in the prior art.

FIG. 6 shows the control characteristics of the power amplifier according to the invention and
Shows AM characteristics.

FIG. 7 shows a GSM time mask defined by GSM Recommendation 05.05 (4.2.2).

FIG. 8 shows a GSM spectral frequency mask defined by GSM Recommendation 05.05 (4.5.2).

Description of the Preferred Embodiment The invention disclosed herein can be used in the TDMA radiotelephone system shown in FIG. In a radiotelephone system, there is a fixed site transceiver 101 that transmits RF signals to portable and mobile radiotelephones contained within a geographic coverage area. One such phone is a portable wireless phone1
03. The wireless telephone system is assigned a frequency band in which transmission is possible. The frequency band is divided into several channels 200 kilohertz wide. Each channel can handle communications between the transceiver 101 and up to eight wireless telephones within its coverage area.
Each wireless telephone is assigned a time slot for transmitting information to the transceiver 101 and receiving information from the transceiver 101. Each time slot is approximately 577 msec second in duration. Portable wireless telephone 103, Motorola
Model number F19UVD available from Incorporated
0960AA with transmitter 107, receiver 109 and DSP56000 available from Motorola, Inc.
Includes a digital signal processor (DSP) 111. Several signals are transmitted between the DSP 111 and the transmitter 107 by a plurality of signal lines 113.

The transmitter 107 and the transceiver 101 are both group Speci
al Mobile (GSM) Recommendation ETSI / PT-12 05.05 (4.2.2 and 4.5.2), March 1991, including power amplifiers that meet stringent requirements. This specification requires that any transmitter conform to the time mask shown in FIG. 7 and the spectral frequency mask shown in FIG.

Antenna 105 is used to transmit and receive radio frequency signals to and from transceiver 101. Upon receiving the signal, antenna 105 converts the signal to an electrical radio frequency signal and forwards the signal to receiver 109. Receiver 1
09 converts the electrical radio frequency signal into a data signal usable by the rest of the portable radiotelephone 103.

In response to the transmission of the radio frequency signal, DSP 111 provides information desired to be transmitted to transmitter 107 and control information for transmitter 107 via signal line 113. Transmitter 1
07 receives the data and converts it to an electrical radio frequency signal and provides an appropriate amount of power to the electrical radio frequency signal by use of a power amplifier. Antenna 105 receives the following electrical radio frequency signals and converts them to radio frequency signals and transmits them over the air for use by transceiver 101.

Power amplifier 203 and its associated controller are located in transmitter 107 and are shown in the block diagram of FIG. The function of the power amplifier 203 is to take the radio frequency input, including data and voice, to be transmitted back to the fixed site transceiver 101 and amplify the RF input signal 209 to the appropriate power for transmission. Exciter 205
Are adjustable power amplifiers that adjust the RF input signal 209 to their appropriate input level for the power amplifier 203.

The block diagram of FIG. 2 includes several control loops, including a standard control loop for a power amplifier, a ramp up loop, and a saturation detection loop. For more information on the power startup loop, see U.S. patent application Ser. No. 07 / 709,738, "Power
Amplifier Ramp Up Method and Apparatus ", Hi
, filed June 3, 1991, and assigned to the assignee of the present invention. A detailed US patent application Ser. No. 07 / 709,737 for the saturation detection loop, “Power Amplifier
Saturation Detection and Correction Method
and Apparatus ", filed June 3, 1991 by Black et al. and assigned to the assignee of the present invention.

The circuit of FIG. 4 is a two-stage power amplifier with variable gain used as exciter 205. First amplification stage 435
Is a transistor 411, a diode 407, an inductor 41
3, including resistors 403,405,409. The second amplification stage 433 includes a transistor 429, a diode 419, an inductor 431, and a resistor 41.
Includes 5,421,422. The two amplification stages are connected together via a direct signal line 417.

Control voltage 425 is used to control the bias current in both amplification stages 433,435. The control voltage is serialized so that it can control the gain of both amplifier stages 433,435 simultaneously. Transistor 423 is 2
A control voltage line 425 is provided between the two amplification stages. The purpose of the transistor 423 is to shift the voltage of the control voltage signal 425 to separate the control characteristic of the first amplifier stage from the second amplifier stage so that the control characteristic 601 of FIG. 6 is obtained. is there. Other equally efficient voltage shifting methods including diodes or voltage divider circuits are also available. The difference of the control voltage 425 with respect to the amplification stages 433,435 is also used to separate the two power amplifier stages 433,435 from the region of the AM characteristic containing the highest AM output. In a preferred embodiment,
The circuit shown in FIG. 4 has a 1% A in the RF input signal 401.
AM less than 2% over the entire power output range for M inputs
Has output. This results in an AM characteristic similar to waveform 603 in FIG. Without shift of control voltage signal 425, A
The magnitude of the M characteristic is almost twice as large at the peak. This can violate the maximum power output required in the GSM spectral time mask shown in FIG.

Transistors 411 and 429 are set up for high power efficiency. The emitters and collectors of these transistors have no loss elements and allow for maximum efficiency. The emitters of both transistors 411 and 429 are directly connected to electrical ground, and the collectors are connected to a power supply via inductors 413 and 431, respectively. Inductors 413 and 431 act as RF loads for the amplifier. Connecting the emitter directly to ground prevents any unnecessary loss of the amplifier, but makes the amplifier unstable over temperature.

Diodes 407 and 419 stabilize the bias current over temperature, isolate the amplifier from RF input signal 401 in the absence of control voltage 425, and provide circuit protection from excessive control voltage 425. First, the diode acts as a bias stabilizer. By matching the diode 407 with the base-emitter characteristics of the transistor 411, the bias current through the transistor becomes stable with temperature for a given control voltage 425 as long as the resistor 405 remains at a small value. Second, diode 407 acts to isolate RF input signal 401 from transistor 411 in the absence of control voltage 425. As the control voltage increases, the diode
The RF input signal is not attenuated while the conductivity of 407 increases, so that there is an active control voltage and current through diode 407. Without control voltage 425, diode 4
The conductivity of 07 is low, separating the RF input signal 401 from the rest of the amplifier circuit. Thus, the amplifier stage has high input-to-output isolation in the absence of a control voltage, giving the amplifier stage a large power control range. Third, the diode 40
7 acts as a protection against excessive control voltage signals.

Resistor 405 acts as a DC return element to diode 407 and as an RF blocking element. Its value should be chosen to match the emitter ballast voltage drop inside transistor 411. Pull-up resistor 403
Is used to provide a reverse bias current to the diode in the absence of control voltage 425, thereby further reducing the conductance of diode 407 and increasing the attenuation of RF input signal 401. This resistor 403 is optional and not necessary for a successful amplifier circuit.

The two amplifier stages are DC coupled together such that the maximum power from the first amplifier stage can be coupled to the second amplifier stage.

Therefore, the circuit shown in FIG. 4 is temperature stable with a large power control range and improved AM output,
Provides a power efficient RF amplifier design.

Continuation of the front page (56) References Japanese Patent Publication No. Sho 45-8042 (JP, B1) US Patent 3560995 (US, A) US Patent 4225827 (US, A) US Patent 4992753 (US, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03G 1/00-3/34 H03F 1/30

Claims (7)

(57) [Claims] A transistor, at least first and second transistors;
A radio frequency amplifier including a first resistor, wherein the amplifier comprises a first
A signal input and a first signal output, wherein the first resistor has first and second ends, the second end is coupled to electrical ground, and the transistor has a base,
An emitter and a collector, the emitter being coupled to electrical ground, the collector being coupled to the first output signal, the base being coupled to a first end of the second resistor, A frequency amplifier, a second variable voltage source coupled to a second end of the second resistor, and a diode having first and second ends, wherein the first end is an anode. Wherein the second end is a cathode and the first end of the diode is coupled to a base of the transistor and to a first end of the second resistor; Is coupled to a first end of the first resistor and to the first signal input, wherein a change in the second variable voltage source causes a corresponding change in the bias current of the diode; Effective conductance of the diode Changing the Nsu, whereby said diode RF switch, RF attenuator and being responsive as a temperature compensation device, a radio frequency amplifier having a. 2. The apparatus of claim 2, further comprising a third resistor having first and second ends, wherein the first end is coupled to the second end of the diode, and wherein the second end is connected to the second end of the diode. A portion coupled to a third voltage source to provide a reverse bias current to the diode in the absence of application of the second variable voltage source;
The amplifier according to claim 1. 3. A transmitter having a control characteristic and including at least first and second means for amplification (435, 433), wherein said first and second means for amplification each comprise a signal. An input, a control signal input, a signal output, and a point having a maximum slope according to the control characteristic according to the control signal input, wherein the transmitter comprises a first means for the amplification and a signal for the amplification. Means (417) for combining the second means of: a control line (425) for receiving a control signal (control voltage) having a voltage, said control line being a line of the first means for said amplification. Coupled to the control signal input, and means for shifting the voltage having the input and the output (423)
Wherein said input of said shifting means is coupled to said control line, said output of said shifting means is coupled to a control signal input of a second means for said amplification, and The point of maximum slope of the control characteristic of one means is shifted from the point of maximum slope of control characteristic of the second means for amplification (603), thereby substantially increasing the maximum slope of the transmitter control characteristic. The transmitter, comprising: 4. The transmitter of claim 3, wherein said signal input of said first and second means for amplification is a radio frequency (RF) signal input. 5. The transmitter according to claim 3, wherein said signal output of said first and second means for amplification is an RF signal output. 6. The means for shifting the voltage comprises a transistor having a base coupled to the control line and an emitter coupled to the control signal input of the second means for amplifying. A transmitter according to claim 3. 7. The method according to claim 1, wherein said means for combining comprises a first
4. The transmitter according to claim 3, further comprising a signal line for coupling a signal output of the second means and a signal input of the second means for amplification.